$5)$At an activity level of $5,500$ units, the cost for maintenance is $$7,100$; at $10,000$ units, the cost for maintenance is $$11,600.$ Using the high$-$low method, what is the cost formula for maintenance?

A$)$$$1\mathrm{.}16$ per unit.

B$)$$$1\mathrm{.}20$ per unit.

C$)$$$600$ plus $$1\mathrm{.}10$ per unit.

D$)$$$1,600$ plus $$1\mathrm{.}00$ per unit.